In recent years, there has been an exponential increase in the use of User Equipment (UEs) such as mobile phones, Personal Digital Assistants (PDAs), pagers, Palmtops™, and laptops. Data transfer or information exchange can be enabled between one or more UEs through a communication network. Examples of a communication network include, but are not limited to, Universal Mobile Telecommunications System (UMTS) networks, General Packet Radio Service (GPRS) networks, Code Division Multiple Access (CDMA) 2000 networks, Worldwide Interoperability for Microwave Access (WiMAX) networks, Digital Subscriber Line (DSL) networks, Wireless Fidelity (WiFi) networks, and cable networks. Some communication networks use a standardized next-generation networking architecture such as an Internet Protocol Multimedia Subsystem (IMS) that can be employed to offer varied services, for example, Voice-over-Internet Protocol (VoIP) and multimedia services. IMS is a services framework to deliver Internet Protocol (IP)-based services that has been proposed by Third-Generation Partnership Project (3GPP) and adopted with minor changes by other standards bodies such as Third-generation Partnership Project 2 (3GPP2), Cable Labs, and Network Working Group of WiMAX. IMS uses Session Initiation Protocol (SIP) as the underlying session protocol. IMS can facilitate various services and applications on the UE, such as presence services, video conferencing, Push-to-talk Over Cellular (PoC), multiparty gaming, community services, and content sharing.
In IMS, two types of identities are implemented for a user, namely, a public user identity and a private user identity. The private user identity, which uniquely identifies a UE to the network, is assigned to the user by the network and is known only to the network and the user of the UE. The private user identity can be stored in the network in a home subscriber server (HSS) and can be used to identify the user's subscription information, such as the user's security-related information. The private user identity also can be stored permanently in an IP Multimedia Services Identity Module (ISIM), which can be encapsulated within the UE. The user's subscription information maintained by the HSS may include one or more private user identities. In addition, typically the ISIM consists of one private user identity, but more than one private user identity in an ISIM is possible. The user's subscription information also can be associated with one or more public user identities.
The public user identity/identities can be used by the user to enable communication with other users. An example of the public user identity/identities can be a SIP URI (Uniform Resource Identifier). Each private user identity of the user can be associated with multiple public user identities.
When the user registers with a network, using the ISIM in the UE, the public user identity, the private user identity, and the IP address of the UE are transmitted to the network, typically via a register message. The network can then use the private user identity provided in the register message to retrieve security credentials of the user from the subscription information in the HSS and hence can authenticate the user. The network can also create a binding of the user's public user identity to an IP address of the UE. This binding information then is used by the network to forward SIP messages to the user's UE based on the user's public user identity. If the UE's IP address changes, for example, when the UE traverses across communication networks, the UE is required to re-register with the network using the new IP address. Typically, the UE sends the same private user identity in the re-registration as the UE had used in the initial registration. On this re-registration, the network removes the older binding of the public user identity and the old IP address and creates a new binding of the public user identity to the new IP address.
The removal of the older binding and creation of a new binding disrupts any ongoing session with the old IP address. Hence, the change in the local IP address can completely disrupt ongoing IMS sessions such as an active call, an instant messaging service, a Bluetooth™ transfer session, a web-browsing service, and a video-streaming service on the UE. Such disruptions greatly impact the user's experience of such services. Therefore, there is a need for a method and system that will enable seamless continuity of IMS sessions when the UE moves across communication networks.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated, relative to other elements, to help in improving an understanding of embodiments of the present invention.